Software defined battery charger system and method

ABSTRACT

A backup battery charging system for a building management system is disclosed. Components of the charging system include an analog power converter, a voltage feedback loop and a current feedback loop. The feedback loops each include at least one digital resistor. The system panel, in turn, includes at least one microcontroller that controls the building management system and also controls the charging system. The charging system is “software defined,” in that the microcontroller controls the charging system by updating the digital resistors in the feedback loops to control the analog power converter. In one example, the building management system is a fire alarm system controlled by a fire control panel as the system panel.

RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/696,641, filed on Sep. 6, 2017, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

Building management systems such as building automation systems, firealarm systems and intrusion detection systems are often installed withinpremises such as in a commercial, residential, or government building.Examples of these buildings include offices, hospitals, warehouses,public infrastructure buildings including subways and bus terminals,multi unit dwellings, schools or universities, shopping malls,government offices, and casinos, to list a few examples.

Fire alarm systems typically include fire control panels that functionas system controllers. Fire detection/signaling devices and alarmnotification devices are then installed throughout the buildings andconnected to the panels. Some examples of fire detection/signalingdevices include smoke detectors, carbon monoxide detectors, flamedetectors, temperature sensors, and/or pull stations (also known asmanual call points). Some examples of fire notification devices includespeakers, horns, bells, chimes, light emitting diode (LED) reader boardsand message boards, and/or flashing lights (e.g., strobes).

During operation of the fire alarm systems, the fire detection devicesmonitor the buildings for indicators of fire. Upon detection of anindicator of fire such as smoke or heat or flames, the device isactivated and a signal is sent from the activated device to the firecontrol panel. The fire control panel then initiates an alarm conditionby activating audio and visible alarms of the fire notification devicesof the fire alarm system. Additionally, the fire control panel will alsosend an alarm signal to a monitoring station, which will notify thelocal fire department or fire brigade.

Intrusion systems typically include intrusion panels and monitoringdevices, where the monitoring devices detect indications of intrusionsand unauthorized access at or within the building and report to theintrusion panel. The monitoring devices of the intrusion systems ofteninclude motion sensor devices, surveillance camera devices, and doorcontrollers that communicate with the intrusion panel over a securitynetwork. Motion sensor devices can detect intrusions and unauthorizedaccess to the premises, and send indications of the intrusions to thesecurity panel. The surveillance camera devices capture video data ofmonitored areas within the premises, and door controllers provide accessto perimeter and/or internal doors, in examples.

Building automation systems will typically include one or more buildingautomation control panels and devices that control and monitor thephysical plant aspects of a building and aspects of business-specificelectrical, computer, and mechanical systems. The physical planttypically includes heating, ventilation, and air conditioning (HVAC)systems, elevators/escalators, lighting and power systems, refrigerationand coolant systems, and air and/or water purification systems, inexamples. Business-specific systems include computer systems,manufacturing systems that include various types of computer-aidedmachinery and test equipment, and inventory control and trackingsystems, in examples.

These building management systems often cannot rely upon the power gridas a sole source of input power. The systems typically employ a backupbattery system that provides a source of backup power to panels in theevent of failure or disruption of the power grid or the connection tothe grid. These backup battery systems will also typically have acharging system for charging of the backup battery system.

SUMMARY OF THE INVENTION

The batteries in the battery backup systems often have extended batterystandby requirements. The standby requirements are dictated bygovernmental safety standards and/or building codes. The batteries mustalso be subjected to mandatory annual battery capacity testing.Maximizing a battery's life requires a charging system that adjustsoutput voltage applied to the batteries in the backup battery systembased on the state-of-charge as well as temperature, and that adjuststhe output current based on battery size and chemistry, and possiblyother requirements.

Major components of traditional charging systems include an analog powerconverter, one or more feedback loops connected to the analog powerconverter, and a controller. The analog power converter provides anoutput current at an output voltage to charge the batteries of thebackup battery systems. Feedback loops are control circuits that havesome or all of its output fed back into its input. The feedback loopsdetect changes to the output, and can respond to changes in the outputthat fall below and/or exceed thresholds by adjusting the input. Thecontroller is typically dedicated to controlling the charging system.

The charging systems typically provide the following base set offeatures. The charging systems provide both a float charge and a fastcharge output voltage with temperature compensation, limit chargingcurrent proportional to battery size, support different batterychemistries, and limit charging voltage based on battery chemistry. Thecharging systems must also operate in a way that maximizes the life ofthe batteries. A set of operating parameters for configuring the powerconverter is built from these features.

Temperature compensation involves adjusting the output voltage that thecharging system applies to the batteries based on the temperature of thebatteries. Cold batteries require a higher charging voltage to sourcecurrent into the batteries, while warmer batteries require a lowercharging voltage for the same purpose. Optimally, temperature sensorslocated in the same space or enclosure as the batteries in the batterybackup system measure the temperature of the batteries. The chargingsystem can then adjust the output voltage applied to the batteries inresponse to the measured temperature.

The charging systems also limit charging current and charging voltagebased upon battery size and battery chemistry, respectively, and supportdifferent battery chemistries. Batteries usually include a number ofindividual cells, where the size of the battery is typically determinedby the number of cells. Example battery chemistries include lead-acid,nickel metal hydride, and lithium. The charging systems typicallyutilize charging profiles for each battery that set a maximum chargingcurrent and a charging voltage for each battery size and chemistry.

Maximizing a battery's life requires a charging system that adjusts itsoutput voltage applied to the batteries. The charging system typicallyadjusts the output voltage based on the state-of-charge (percentcharged) as well as temperature. When a battery is depleted and beingrecharged it will accept charge at a faster rate if the charging voltageis increased. This increased voltage can only be applied for a shorttime otherwise damage and reduced life would result. As a resultchargers can be designed to have a ‘fast’ charging voltage duringrecharge and a lower ‘float’ voltage for extended shelf-life.

However, designing charging systems to provide the base set of featuresis complex and costly, prompting manufacturers to make designcompromises to reduce complexity and/or cost. In one example, ratherthan setting the output current that is appropriate for each batterysize, some charging systems provide only two output current levels,appropriate for “small” and “large” sizes of batteries. In anotherexample, some charging systems use a single output voltage for both thefast charging and float charging modes. This can increase recharge cycletimes and/or reduce battery life. Some charging systems require anoperator to manually configure the output voltage for each batterychemistry, or support only one type of battery chemistry. Yet othersystems make compromises with regards to temperature compensation, suchas compensating for temperature only during fast charging mode or notcompensating for temperature at all.

Some charging systems use a digital microcontroller as the controller,where the digital microcontroller is combined with a power converter inone integrated circuit (IC) module. Applications such as softwareperipherals can then submit all operating parameters for configuring thepower converter to the module. This results in a tightly integrateddesign with a small bill of materials. However, these integrated circuitmodules are highly specialized and expensive. Moreover, because theentire power converter is defined in software, it has many time-criticaloperations to perform. If the microcontroller is used for otherpurposes, the application will find it has fewer available resources andthere may be timing conflicts between operating the power converter andperforming other actions.

An inventive charging system, such as for a building management system,is proposed. Specifically, the charging system is under control of atleast one microcontroller of the system panel, for example. Themicrocontroller of the system panel (“microcontroller”), for example,provides the functionality of the dedicated controller in traditionalcharging systems, in one example. As a result, the dedicated controllerof the traditional charging system is no longer needed, which reducescharging system complexity and manufacturing cost.

The inventive system also includes a battery backup system that ischarged by the charging system. The battery backup system provides asource of power for the system panel. The charging system charges thebatteries in battery backup system via an analog power converter of thecharging system. The analog power converter provides an output currentand output voltage to the battery backup system under control of themicrocontroller.

The microcontroller maintains charging profiles for the batteries in thebattery backup system. The charging profiles define a charging mode(e.g. fast and/or float charging modes), a target voltage, and targetcurrent at the target voltage. The target voltage defines an outputvoltage and the target current defines a maximum output current for theanalog power converter of the charging system to apply to the batterybackup system. The value of the output voltage is based on the chemistryof the batteries, and the value of the output current is based upon asize of the batteries. The charging profiles also maintain a table oftemperature compensation voltages for adjusting the output voltage. Thetable includes values of compensation voltages for differenttemperatures, in accordance with temperature compensation curves foreach battery chemistry.

In general, according to one aspect, the invention features a batterybackup system and a charging system, of a building management systemhaving a system panel, for example. The charging system charges thebattery backup system, and includes an analog power converter. Theanalog power converter preferably provides an output current at anoutput voltage to the backup battery system under control of amicrocontroller.

In one example, the system panel is a fire control panel, and the firecontrol panel is included within a fire alarm system that operates asthe building management system.

The microcontroller can additionally control a detection circuitincluding sensor devices, and can control a notification circuitincluding notification devices. The microcontroller can also monitor apower bus that provides a primary source of input power to the systempanel, and can send notifications to a central station in response toreceiving indications of fire from the fire sensor devices.

The microcontroller preferably stores one or more charging profiles forthe charging system. The microcontroller applies the charging profilesto the backup battery system for charging the backup battery system.Typically, the charging profiles include a target voltage, a targetcurrent, and a temperature compensation table. The target currentdefines a maximum output current. The temperature compensation table, incontrast, provides a temperature compensation voltage based upon atemperature of batteries in the backup battery system.

Typically, the target voltage within each charging profile is based onchemistry of the batteries within the backup battery system, and thetarget current within each charging profile is based on a size of thebatteries within the backup battery system.

The microcontroller can also control the output voltage by updating aregister within an output voltage digital resistor of a voltage feedbackloop of the charging system.

Additionally and/or alternatively, the microcontroller can receive atemperature measurement of the backup battery system, obtain atemperature compensation voltage based upon the measured temperature,and then update the register within the output voltage digital resistorbased upon the temperature compensation voltage. The microcontrollerpreferably receives the temperature measurement from a temperaturesensor located within the backup battery system.

Additionally and/or alternatively, the microcontroller can control theoutput current by updating a register within an output current digitalresistor of a current feedback loop of the charging system.

In general, according to another aspect, the invention features a methodfor a building management system. The method comprises a system panelcontrolling the building management system, a backup battery systempowering the system panel, and a charging system charging the backupbattery system. The system panel includes at least one microcontroller,and the at least one microcontroller controls an analog power converterof the charging system to provide an output current at an output voltageto the backup battery system.

The charging system can also measure errors in the output voltage and/oroutpit current, and correct the errors.

The at least one microcontroller can control the analog power converterof the charging system to provide the output current at the outputvoltage to the backup battery system. In one example, the at least onemicrocontroller can control the analog power converter by: receiving atemperature measurement of the backup battery system; obtaining atemperature compensation voltage based upon the measured temperature anda target voltage maintained by the microcontroller; and updating aregister within an output voltage digital resistor of a voltage feedbackloop of the charging system with a resistor setting. The resistorsetting is preferably based upon the target voltage offset by thetemperature compensation voltage.

In one implementation, the microcontroller obtains the temperaturecompensation voltage in response to the microcontroller executing alookup of the measured temperature from a temperature compensation tablemaintained by the microcontroller.

Additionally and/or alternatively, the at least one microcontroller cancontrol the analog power converter of the charging system to provide theoutput current at the output voltage to the backup battery system. Theat least one microcontroller can control the analog power converter by:calculating a resistor setting based on a target current maintained bythe microcontroller; and updating an output current digital resistorwithin a current feedback loop of the charging system with the resistorsetting. The target current defines a maximum value for the outputcurrent.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1A shows an embodiment of a fire alarm system as an example of abuilding management system installed at a premises, where the fire alarmsystem is controlled by a fire alarm panel and includes a chargingsystem for charging a backup battery system that provides power to thefire control panel, and where a microcontroller of the fire controlpanel controls the operation of the charging system;

FIG. 1B shows another embodiment of a fire alarm system including a firecontrol panel as in FIG. 1A, where the microcontroller of the firecontrol panel also controls the operation of the charging system;

FIG. 2 shows detail of a charging profile maintained by themicrocontroller of the fire alarm panel in FIGS. 1A and 1B for aspecific backup battery system;

FIG. 3 and FIG. 4 are exemplary configurations of an output voltagedigital resistor and an output current digital resistor within thecharging systems included in FIGS. 1A and 1B; and

FIG. 5 is a flow chart that describes a method of operation for themicrocontroller for controlling an analog power converter of thecharging system in FIGS. 1A and 1B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Further, the singular formsof the articles “a”, “an” and “the” are intended to include the pluralforms as well, unless expressly stated otherwise. It will be furtherunderstood that the terms: includes, comprises, including and/orcomprising, when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. Further, it will be understood that when anelement, including component or subsystem, is referred to and/or shownas being connected or coupled to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent.

FIG. 1A shows a fire alarm system 100. The fire alarm system 100 is anexample of a building management system at a premises, such as abuilding 90. The fire alarm system 100 includes a charging system 10, afire control panel 70, and a backup battery system 32. The chargingsystem 10 charges the backup battery system 32, which in turn powers thepanel 70. The backup battery system 32 provides a source of power to thepanel 70 when a main source of AC power 89 to the panel 70 is disruptedor unavailable.

The panel 70 includes a number of interfaces 128-1 through 128-4, amicrocontroller 40, and a central processing unit (CPU) 18. Of theinterfaces 128, power monitor interface 128-1 connects to a power bus 13to which the AC power 89 connects. Telephony interface 128-2 connects toa Plain Old Telephone System (POTS) 19 that in turn connects to acentral station 138. Detection circuit interface 128-3 connects todetection circuit 84. Notification circuit 128-4 connects to anotification circuit 94.

The microcontroller 40 is preferably a self-contained computer systemhaving one or more programmable interfaces, one or more analog todigital input ports, and one or more digital to analog output ports. Itfurther has memory and one or more processors/processor cores.

According to the embodiment, the microcontroller 40 further stores oneor more charging profiles 54 and has an Analog to Digital (A/D)converter 27. The microcontroller 40 also communicates with the CPU 18and interfaces 128 of the panel 70. In examples, the microcontroller 40handles monitoring for AC power 89, earth faults, manages the detectionand notification circuits 84/94, reports fire alarm status to municipalfire departments via the telephony interface 128-2, reports to the CPU18, and manages the flow of power through the fire control panel 70.Most of these are time-sensitive functions, especially the communicationwith the main system CPU 18.

The charging system 10 in conjunction with the microcontroller 40provide the base set of features of traditional charging systems. Thecharging system 10 also does not compromise different aspects of itsdesign as some traditional charging systems do.

The detection circuit 84 includes one or more fire detection/initiationdevices 111-1 and 111-2 that detect an indication of fire such as heat,flame and/or smoke, and a pull station 85. The fire detection/initiationdevices 111 send signals in response to detecting an indication of fireto the panel 70. The fire detection/initiation devices 111 send thesignals via the detection circuit interface 128-3. When activated by anindividual, the pull station 85 sends an emergency signal over thedetection circuit 84 and the panel 70 receives the signal via itsdetection circuit interface 128-3 in a similar fashion.

The notification circuit 94 includes one or more notification devices121. In response to receiving signals indicative of fire or an emergencycondition from the detection circuit 84, the panel 70 sends signals overthe notification circuit 94 to activate the notification devices 121 toalert occupants at the premises 90, such as activating a strobe alarmnotification device 121-1 and a siren alarm notification device 121-2.

The backup battery system 32 includes one or more batteries and atemperature sensor 42 that measures a temperature 124 of the batteries.In one implementation, the temperature sensor 42 is a thermistor orother passive device. The microcontroller 40 reads a voltage across thethermistor via its A/D converter 27 at regular intervals, and themicrocontroller 40 converts the detected voltages to a temperature 124.In another implementation, the microcontroller 40 obtains thetemperature 124 by polling the temperature sensor 42, typically on theorder of tenths of a second. In yet another implementation, the chargingsystem 10 polls the temperature sensor 42 for the temperaturemeasurement 124 and sends the temperature measurement 124 to themicrocontroller 40.

The charging system 10 includes components such as a primary powersource 20, an analog power converter 22, a current sensing circuit 30,an error amplifier 26, a voltage feedback loop 50 and a current feedbackloop 60. The voltage feedback loop 50 controls the analog powerconverter 22 by comparing the output voltage versus a reference andadjusting the power converter 22 proportionally to the error. Thecurrent feedback loop 60 controls the analog power converter 22 byadjusting the maximum output current Iout. In one implementation, thevarious components of the charging system 10 are arranged on a printedcircuit board (PCB) and are electrically connected via traces of thePCB. The traces are made of aluminum, copper or other electricallyconductive material, in examples.

The current sensing circuit 30 is connected in series between the analogpower converter 22 and the backup battery system 32. The analog powerconverter 22 connects to the current sensing circuit 30 via outputconnection 35. In one example, the output connection 35 is a printedcircuit trace. The output current Iout at the output voltage Vout flowsfrom the analog power converter 32 through the current sensing circuit30. Iout then flows to the backup battery system 32 for charging thebatteries of the backup battery system 32.

In many traditional charging system designs, the power converter is aone-way power converter that either steps up (boosts) or steps down(bucks) its primary power source to create the desired output voltageand output current. If the primary power source is at roughly the samevoltage as the batteries of the backup battery system, a Buck/Boostconverter can be used; however they are usually avoided due to cost andcomplexity. Buck and boost converters are typically created by using atransistor to connect and disconnect an energy storage element like aninductor into a rectified filtering network that averages this on-offaction into a constant DC output. The output power is a function of thepercentage of time each cycle that the transistor is on versus off in amethod called Pulse Width Modulation. Switching power converters (asthese are called) are designed to minimize the energy wasted to heatduring the conversion of one voltage and current into another.Buck-style battery chargers can also be made using a ‘linear’ converterwhere the voltage difference between input and output is simply spent aswaste heat; however, any battery charger with this level of complexitywill almost certainly be a ‘switching’ converter.

The voltage feedback loops of traditional charging systems sample theoutput voltage provided by the analog power converter, using aproportional voltage created by a resistive voltage divider. A voltagedivider is a passive linear circuit that includes two or more resistorsin series, where the output voltage is a fixed fraction of its inputvoltage. However, because the voltage dividers have fixed resistancevalues, the analog power converters in the traditional charging systemsmake the same output.

Traditional charging systems also often support temperature compensationby using a temperature dependent resistor inside the voltage feedbackloop. This has drawbacks, however. The temperature dependent resistor islocated near the normally hot circuitry of the voltage feedback loop andpower converter, rather than being remotely located with the batteriesof the battery charging system. Moreover, the temperature dependentresistors usually have exponential response curves, while the voltageand current feedback loops are linear circuits.

Returning to FIG. 1A, a portion or all of the resistive voltage dividersof traditional charging systems are replaced with digital resistors inthe charging system 10 of the proposed building management system 100.Digital resistors are digitally-controlled integrated circuits thatgenerate an output resistance value in response to programmed input. Theinput is a resistor setting that is included within a message sent tothe digital resistor. The voltage feedback loop 50 includes at least oneoutput voltage digital resistor 24 and the output current feedback loop60 includes at least one output current digital resistor 34.

In more detail, the voltage feedback loop 50 includes at least oneoutput voltage digital resistor 24 that receives resistor settings 23calculated by and sent from the microcontroller 40. The microcontroller40 updates the resistor setting 23 to control the output voltage Vout.In response to receiving the resistor setting 23, the output voltagedigital resistor 24 produces a resistance value that modifies thevoltage feedback loop 50. The voltage feedback loop 50, in turn, adjuststhe output voltage Vout. In one implementation, the output voltagedigital resistor 24 is configured as a rheostat for adjusting the outputvoltage Vout.

The current feedback loop 60 includes a non-inverting operationalamplifier (op amp) 48 and at least one output current digital resistor34 that receives resistor settings 33 calculated by and sent from themicrocontroller 40. Inputs of the op amp 48 connect to the currentsensing circuit 30 and the output current digital resistor 34, and theoutput of the op amp 48 connects to the error amplifier 26. Themicrocontroller 40 updates the resistor setting 33 to control the gainof the current sensing circuit. By adjusting the gain of the op amp 48,the output current Iout can be adjusted to any level required.

Because the microcontroller 40 controls the charging system 10 byupdating digital resistors 24/34 in the voltage and current feedbackloops 50/60, respectively, the charging system 10 is also known as asoftware defined charging system.

FIG. 1B also shows a fire alarm system 100. FIG. 1B includes allcomponents as in FIG. 1A, and the fire alarm system 100 operates in asimilar fashion as in FIG. 1A. However, the charging system 10 and thefire control panel 70 include additional features not found in FIG. 1A.In examples, the additional features include the ability to monitor theoutput current Iout and the output voltage Vout, and to adjust Iout andVout for errors.

The voltage feedback loop 50 provides a sampled version of the outputvoltage Vout, indicated by reference 56. The current sensing circuit 30provides a sampled version of the output current Iout, indicated byreference 66. The sampled output voltage 56 and sampled output current66 are received by the A/D converter 27 of the microcontroller 40. In apreferred implementation, the charging system 10 provides the sampledoutput voltage 56 and sampled output current 66 on a periodic basis tothe microcontroller 40. However, the microcontroller 40 can also pollthe charging system 10 for these values. The microcontroller 40 uses thesampled output voltage 56 and sampled output current 66 to adjust forerrors in the output voltage Vout and output current Iout. In this way,the charging system 10 of FIG. 1B can measure errors in the outputvoltage Vout and output current Iout, and correct these errors.

In one implementation, the microcontroller 40 receives an errorcorrection flag 82 sent from a user on a computer system. The errorcorrection flag 82 normally has a value of false. Possible sources oferror that can cause the error correction flag 82 to have a value oftrue include: resistors with inconsistent values in production, andlosses through other components, traces, cables, or connectors, inexamples. Based upon the value of the flag 82 (e.g. true or false), themicrocontroller 40 can modify its operation to select between thefunctionality for controlling the charging system 10 of the fire alarmsystem 100 of FIG. 1A (when the flag 82 is false) and for the chargingsystem 10 of the fire alarm system 100 of FIG. 1B (when the flag 82 istrue).

FIG. 2 includes an exemplary charging profile 54 included within/storedby the microcontroller 40 for the charging system 10. Themicrocontroller 40 applies charging profiles 54 to the backup batterysystem 32 for charging batteries in the backup battery system 32.

Backup battery systems 32 preferably include batteries of the same sizeand battery chemistry. The microcontroller 40 maintains a separatecharging profile 54 for each size and battery chemistry supported by thecharging system 10, i.e. for each backup battery system 32 havingspecific battery size and battery chemistry requirements.

Each charging profile 54 includes a battery ID 102, a target voltage122, a target current 132, a charging mode 104 and a temperaturecompensation table 146. The battery ID 102 is associated with thespecific battery size and chemistry of batteries in each battery backupsystem 32 that the charging system 10 supports. The target voltage 122defines a value for the output voltage Vout that the analog powerconverter 22 applies to the backup battery system 32, while the targetcurrent 132 defines a maximum value for the output current Iout that theanalog power converter 22 can apply to the backup battery system 32. Thetarget voltage 122 is based on chemistry of the batteries within thebackup battery system 32 and the charging mode 104. The target current132 is based on a size of the batteries (e.g. number of cells) and thecharging mode 104.

The charging mode 104 is a field that indicates the current mode forcharging the backup battery system 32. Fast charge and float chargingmodes are typically supported. Fast charging mode selects a higher valuefor the target voltage 122, for faster charging of the batteries of thebackup battery system 32. In contrast, float charging mode selects alower value for the target voltage 122, for maintaining fully chargedbatteries for extended lifetimes. In one example, an operator canconfigure the charging mode 104.

The microcontroller 40 receives a temperature 124 measured by and sentfrom a temperature sensor 42 of the backup battery system 32, andmaintains a temperature compensation table 146. The temperaturecompensation table 146 incorporates data of temperature compensationcurves for the supported size and battery chemistry of the batteries. Atemperature compensation table 146 is typically included within eachcharging profile 54. The table 146 provides a temperature compensationvoltage 126 for adjusting the output voltage Vout, based upon thetemperature 124 of the batteries in the backup battery system 32 and thetarget voltage 122.

FIG. 3 shows detail for an output voltage digital resistor 24 of thevoltage feedback loop 50 in the charging systems 10 in FIGS. 1A and 1B.The output voltage digital resistor 24 includes a register 99.

Output voltage digital resistor 24 includes a few or many resistors R1 .. . RN that form a series chain of resistors, and includes a series ofswitches S1 . . . SN. The series chain of resistors is also known as aresistor ladder 98. Each switch SN controls an individual resistor RN.In one example, the resistor setting 23 specifies an on/off switchsetting for each of the switches S1 . . . SN. When a switch SN is set toits “on” setting, the corresponding resistor RN is connected to theresistor ladder 98.

When the digital resistor 24 receives an updated resistor setting 23from the microcontroller 40, the digital resistor 24 stores the resistorsetting 23 to its register 99. The digital resistor 24 then configuresits resistor ladder according to the configuration of the switchesindicated by the resistor setting 23.

Within the voltage feedback loop 50, the output voltage digital resistor24 provides a resistance value that modifies the resistance of thevoltage feedback loop 50. This, in turn, adjusts the output voltageVout.

The output voltage digital resistor 24 can be configured as apotentiometer or rheostat, based upon how the output voltage digitalresistor 24 is connected to the charging system 10. Here, the outputvoltage digital resistor 24 is connected to the output cabling 35 of theanalog power converter 22 and the error amplifier 26 of the chargingsystem 10.

If the output connector 35 of the analog power converter 22 is connectedto one of the ends of the chain of resistors in the output voltagedigital resistor 24, the digital resistor 24 is configured as a variableresistor, sometimes called a rheostat. If instead the output cabling 35is connected as a 3rd terminal of the chain (e.g. the wiper) and theother end is connected to ground, as in FIG. 3, a proportional voltagebetween the two ends of the chain results and this is called apotentiometer. The wiper of the output voltage digital resistor 24 isconnected to the error amplifier 26 of the charging system 10.

FIG. 4 shows detail for an output current digital resistor 34 of thecurrent feedback loop 60 in the charging systems 10 in FIGS. 1A and 1B.The output current digital resistor 34 includes a register 99 that isupdated by the microcontroller 40 with a resistor setting 33 andfunctions in a substantially similar way as the output voltage digitalresistor 24 in FIG. 3.

As with the output voltage digital resistor 24 in FIG. 3, the outputcurrent digital resistor 34 can be configured as a potentiometer orrheostat, based upon how the output current digital resistor 34 isconnected to the charging system 10. Here, the output current digitalresistor 34 is connected to the non-inverting op amp 48 of the chargingsystem 10. In FIG. 4, for example, the output voltage digital resistor34 is configured as a potentiometer, where a non-grounded end of theoutput current digital resistor 34 is connected to a negative terminalof the op amp 48 and a wiper of the output current digital resistor 34is connected to a negative terminal of the op amp 48.

Within the current feedback loop 60, the output current digital resistor34 provides a resistance value that modifies the gain of the currentfeedback loop 60. This, in turn, adjusts the output current Iout.

FIG. 5 is an exemplary method of operation for the microcontroller 40 ofthe fire control panel 70 in the fire alarm systems 100 of FIGS. 1A and1B. The method starts at step 502.

In step 504, the microcontroller 40 receives an error correction flag 82and optional charging mode 104 (e.g. fast charge/float charge) from anoperator on a computer system. Float charge is the default chargingmode. In one implementation, the value of the error correction flag 82(e.g. true or false) is a mechanism for an operator to select betweenthe capabilities provided by the charging systems 10 of FIG. 1A (false)and FIG. 1B (true).

Additionally and/or alternatively, in another example, themicrocontroller 40 can change the state of the error correction flag 82in response to the available and/or current use of resources in themicrocontroller 40. For example, the microcontroller 40 can set thevalue of the error correction flag 82 to false in order to conserveresources. Such a feature is useful when the microcontroller 40 isespecially busy executing other higher priority tasks, such as receivingand processing indications of fire sent from multiple fire sensordevices 111 during an active emergency, in one example.

According to step 506, the microcontroller 40 accesses one or morecharging profiles 64 for the battery backup system 32 and determines acharging profile 54 that is appropriate based on the battery backupsystem 32. In step 508, the microcontroller 40 selects a target voltage122 and target current for 132 charging the battery backup system 32from the charging profile(s) 54, where the target voltage 122 is basedon factors including battery chemistry and charging mode 104, and wherethe target current 132 is based on factors including battery size andcharging mode 104. The target voltage/target current 122/132 define amaximum value for the output voltage Vout and maximum value for theoutput current Iout, respectively.

Then, in step 510, the microcontroller 40 queries a temperature sensor42 such as a thermistor attached to batteries of the battery backupsystem 32 and receives a temperature measurement 124 in response.Alternatively, the charging system 10 can periodically obtain thetemperature 124 of the batteries in the battery backup system 32 bypolling the temperate sensor 42 and sending the temperature measurement124 to the microcontroller 40.

In step 512, the microcontroller 40 calculates a resistor setting 23 forthe output voltage digital resistor 24, where the resistor setting 23 isbased upon the target voltage 122 offset by a temperature compensationvoltage 126. The temperature compensation voltage 126 is preferablyobtained in response to the microcontroller 40 executing a lookup of themeasured temperature 124 from the temperature compensation table 146maintained by the microcontroller 40 within the charging profile 54.

In step 514, the microcontroller 40 calculates a resistor setting 33 forthe output current digital resistor 34, where the resistor setting 33 isbased upon the target current 132 in the selected charging profile 54.In step 516, the microcontroller 40 determines whether the errorcorrection flag 82 is set. If the error correction flag 82 is not set(e.g. is false), which corresponds to the charging system 10 of FIG. 1A,the method transitions to step 522. If the error correction flag 82 isset (e.g. is true), which corresponds to the charging system 10 of FIG.1B, the method transitions to step 518.

In step 518, the microcontroller 40 receives the sampled output voltage56 and sampled output current 66 of the analog power converter 22 fromthe charging system 10 of FIG. 1B. Then, in step 520, themicrocontroller 40 calculates a difference between the target voltage122 and sampled output voltage 56 and a difference between the targetcurrent 132 and sampled output current 66. In response to detectingdifferences that exceed a predefined error threshold, themicrocontroller 40 can then recalculate the resistor setting(s) 23/33for correcting the output voltage Vout and/or output current Iout. Themethod then transitions to step 522.

In step 522, the microcontroller sends resistor setting 23 to the outputvoltage digital resistor 24 to update its register 99. The outputvoltage digital resistor 24, in response, stores the received resistorsetting 23 (e.g. within the register 99 or in non-volatile memory) andconfigures a resistance value for possibly adjusting the output voltageVout.

According to step 524, the microcontroller sends resistor setting 33 tothe output current digital resistor 34 to update its register 99. Theoutput current digital resistor 34, in response, stores the receivedresistor setting 33 (e.g. within the register 99 or in non-volatilememory) and configures a resistance value for possibly adjusting theoutput current Iout. Upon completion of step 524, the method transitionsto the beginning of step 510, which enables the microcontroller 40 tocontinue its control of the analog power converter 22.

It is important to note that the amount of resources that themicrocontroller 40 uses for controlling the charging system 10 isnegligible compared to the amount of resources that the microcontroller40 typically uses to monitor and control other components of thebuilding management system 100. In one example, the microcontroller 40typically polls the power bus 13 on the order of tens of milliseconds todetect potential power disruptions. In contrast, the microcontroller 40typically executes the tasks associated with controlling the chargingsystem 10 on the order of once a second or slower.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A power system, comprising: a backup batterysystem; a microcontroller; and a charging system for charging the backupbattery system, including an analog power converter that provides anoutput current at an output voltage to the backup battery system undercontrol of the microcontroller, wherein the microcontroller controls theoutput voltage by updating a voltage register within an output voltagedigital resistor of a voltage feedback loop of the charging system. 2.The system of claim 1, wherein the microcontroller stores one or morecharging profiles for the charging system to apply to the backup batterysystem for charging the backup battery system, and wherein the chargingprofiles include: a target voltage, and a target current for defining amaximum output current; and a temperature compensation table thatprovides a temperature compensation voltage based upon a temperature ofbatteries in the backup battery system.
 3. The system of claim 2,wherein the target voltage within each charging profile is based onchemistry of the batteries within the backup battery system.
 4. Thesystem of claim 2, wherein the target current within each chargingprofile is based on a size of the batteries within the backup batterysystem.
 5. The system of claim 1, wherein the microcontroller controlsthe output current by updating a current register within an outputcurrent digital resistor of a current feedback loop of the chargingsystem.
 6. The system of claim 1, wherein the microcontroller receives atemperature measurement of the backup battery system, obtains atemperature compensation voltage based upon the measured temperature,and updates the register based upon the temperature compensationvoltage.
 7. The system of claim 6, wherein the microcontroller receivesthe temperature measurement from a temperature sensor located within thebackup battery system.
 8. A power system, comprising: a backup batterysystem; a microcontroller; and a charging system for charging the backupbattery system, including an analog power converter that provides anoutput current at an output voltage to the backup battery system undercontrol of the microcontroller, wherein the microcontroller controls theoutput current by updating a register within an output current digitalresistor of a current feedback loop of the charging system.
 9. A methodfor providing backup power, comprising: a backup battery system poweringbackup power; a charging system charging the backup battery system; andat least one microcontroller controlling an analog power converter ofthe charging system to provide an output current at an output voltage tothe backup battery system by the microcontroller updating a registerwithin an output voltage digital resistor of a voltage feedback loop ofthe charging system.
 10. The method of claim 9, further comprising thecharging system measuring errors in the output voltage and/or outputcurrent, and correcting the errors.
 11. The method of claim 9, furthercomprising storing one or more charging profiles for the backup batterysystem, the one or more charging profiles including a target currentbased on a size of batteries within the backup battery system, thetarget current defining a maximum value for the output current.
 12. Themethod of claim 9, further comprising the at least one microcontroller:monitoring a power bus that provides a primary source of input power toa life safety system; and sending notifications to a central station inresponse to receiving indications of a life safety event.
 13. The methodof claim 9, wherein the at least one microcontroller controlling theanalog power converter of the charging system to provide the outputcurrent at the output voltage to the backup battery system furthercomprises: receiving a temperature measurement of the backup batterysystem; obtaining a temperature compensation voltage based upon themeasured temperature and a target voltage maintained by themicrocontroller, and updating the register within the output voltagedigital resistor with a resistor setting, the resistor setting beingbased upon the target voltage offset by the temperature compensationvoltage.
 14. The method of claim 13, further comprising themicrocontroller obtaining the temperature compensation voltage inresponse to the microcontroller executing a lookup of the measuredtemperature from a temperature compensation table maintained by themicrocontroller.
 15. The method of claim 13, wherein the at least onemicrocontroller controlling the analog power converter of the chargingsystem to provide the output current at the output voltage to the backupbattery system comprises the microcontroller updating a current registerwithin an output current digital resistor of a current feedback loop ofthe charging system.
 16. A method for providing backup power,comprising: a backup battery system powering backup power; a chargingsystem charging the backup battery system; and at least onemicrocontroller controlling an analog power converter of the chargingsystem to provide an output current at an output voltage to the backupbattery system by the microcontroller updating a register within anoutput current digital resistor of a current feedback loop of thecharging system.
 17. The method of claim 16, further comprising themicrocontroller calculating a resistor setting based on a target currentmaintained by the microcontroller, the target current defining a maximumvalue for the output current; and updating the output current digitalresistor with the resistor setting.